Circuit arrangement for selecting a telephone extension by selector keys



Dec. 30, 1969 w. scHuBERTH 3,487,171

ELEPHONE CIRCUIT ARRANGEMENT FOR SELECTING A T EXTENSION BY SELECTORKEYS Filed Oct. 2l. 1965 ma NS @m U @Q uw r, 5w h mkw vb v @www I Il-ll@N Q Nh h l E WN mi .wb

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United States Patent Office Patented Dec. 30, 1969 U.S. Cl. 179--18 4Claims ABSTRACT OF THE DISCLOSURE Each extension station in an automatictelephone system is equipped with four push buttons two in series witheach speech wire. Removal of a receiver will cause relays to couple tospeech Wires and to a source of positive and negative half-waves. Therelays are by-passed by rectiers to respond to either positive ornegative halfwaves. When one push button is depressed, contacts are:closed through one of the relays which operates to establish the firststage of a connection to the called station. Release of the rst pushbutton and depression of another completes the connection by operationof another relay.

The invention relates to circuitry for key-controlled telephone systemsand particularly for relatively small subscribers systems with extensionstations. It is an object of the invention to enable a selection by keysbetween at least ten different lines by remote control with very simplemeans. Different from the previously known key-operated selectors theselecting signals are not audiofrequency signals generated in eachextension station by a separate audiofrequency generator and transmittedto the receiver in the central station. Instead the central stationequipment transmits a general selection signal to the controllingextension station where digit keys are operated to modify thisselect-ion signal for utilization by the receiving equipment in thecentral station.

The circuitry according to the invention differs also from thepreviously known key selection methods using direct current mainly inthat in the latter the polarity of the control wires is sensed inchronological succession by complicated and expensive relay devicesWhereas the invention uses low-frequency alternating current which ise.g. derived from the public supply system and stepped down as a controlcurrent or general selection signal so that the previously requiredexpenditure is avoided.

Another advantage of this circuitry is the direct setting of theline-selecting relays. This enables the selective connection of' up toten two-wire lines to the central station equipment by only four relays.

The circuitry enables also the selection of one of ten extensionstations by the use of only four keys in each extension station providedthat the connection to each of the extension stations is established bytwo key depressions. Each key has only a single change-over Contact.

The circuitry according to the invention for selecting a conversationpartner by selecting keys is characterized in"that an `alternatingcurrent source is provided in the central station and twoseries-connected selecting key contacts are provided in each speech wirein each extension station, the voltage of the alternating current sourceis applied to each speech wire by a contact, which is indirectly closedby the depression of any desired selecting key, and two relayslassociated with each wire and bypassed each by a rectifier, whichrectiers are connected in phase opposition, and the alternating currentflows through the respective closed selecting key contacts and one oftwo phase-opposed rectiers back to the alternating current source, sothat the closing of a certain selecting key contact causes a certainrelay to pick up and prepare the speech channel with its Contact (afterthe first depression of a key) and to establish the speech channel(after the second depression of a key).

Further according to the invention, the central station is provided Witha relay which is responsive to the alternating current source andconnected in the diagonal of a rectifying bridge.

Further according to the invention, an engaging relay energiZa-ble bythe cradle s-Witch, a time-limit relay, a changeover rel-ay, a rel-ayfor signalling the first selection and a relay for signalling the secondselection are provided.

Finally, in accordance with the invention, each of the selecting relayshas a second winding, which is self-holding by a separate contact duringthe conversation. The alternating current source is preferably thelighting supply system (50 Hz).

FIG. 1 shows the application of the invention to a subscribers systemwith ten extensions.

When the receiver in one of the extension stations is lifted, the finderis adjusted to this extension station. (The adjusting means are notshown). The windings SPI and SPII of relay SP are energized through theextension station loop and relay V through the contact sp1. It may beassumed, for instance, that the extension station 34 is selected from anextension station TN. In extension station TN, the key 3T is brieflydepressed. This will interrupt the speech loop and cause the relay SP todrop out. Relay U is energized through contacts sp3. By contacts u1 andu2, relays A and B are connected to the a-wire and relays C and D to theb-Wire. As relay V is energized, the general selection signal consistingof 4an A.C. Voltage of 50` cycles is applied to the speech wires bycontact V1 and the four relay windings AI, BI, CI and DI.

The subsequent explanations are based on the following definition: Whenthe speech Wires carry a control current generated by the transformer TRand flowing from the central station to the extension station, referencewill be made to a positive half-wave. A current in the oppositedirection, from the extension station to the central station, will bedened as a negative half-wave. As is apparent from FIG. 1, the four keys1T, 2T, 3T, 4T offer four different mutually exclusive possibilities.

When 1T is depressed, the positive half-wave can become effective on thea-wire and relay A will pick up because in this case B isshort-circuited by G14. The bwire is interrupted. C and D cannot beenergized.

(l) TR, G18, X, G19, v1, G1 4, AI, u1, AS-a, 2T 1T, G1 1,

When 2T is depressed, the negative half-wave becomes effective on thea-wire. The b-wire is interrupted. Only relay B picks up:

When 3T is depressed, the a-wire is disconnected and the positivehalf-wave of the general selection signal can become effective on theb-Wire. Relay C picks up:

(3) TR, G18, X, G19, v1, G16, CI, us, AS-b, 4T 3T, G11, ground.

Finally when 4T is depressed, relay D picks up:

We will now revert to our example. Key 3T is depressed so that relays Cand X have picked up in circuit (3). Relay X serves for indicatingwhether a key is depressed and is energized as long as any of the fourkeys 1T to 4T is depressed.

Contact x3 energizes relay SP in SPIII and holds U in UII because thefirst winding of U is de-energized when sp3 is open.

When key 3T is released, X and U drop out in this succession. The finalselector relay C holds itself lby its own contact c1 and winding CII.

V does not drop out during the selecting operation `because its releaseis delayed by K1 and R4 and because it is held by the contact x1immediately when X has picked up. The release of relay U is delayed byG111. This delay of the release is required to ensure an energization ofrelay R after the first depression of a key. Relay R is energizedthrough x2 in its inoperative position and through uS n its operativeposition and holds by its own contact r2.

Thus, relay R records that the first selection has been performed. Atthis time, relays SP, V, C, R are energized. Now the key 4T isdepressed. When SP has dropped out and U has picked up, the relays X andD are energized in circuit (4). Relay S is energized through the closedcontact r1 to indicate that the second selection has been performed.

S is held by its own contact:

When key 4T of TN is now released, X and U will drop out. Relays SP, V,C, D, R, S are energized, Thus, the connection to the extension station34 by contacts s1, a3; and s2, n4 is not established until key 4T hasbeen released.

(9) aawire, s1, 113, a2, b3, c4, d4, a-wire to extension station 34,telephone apparatus of extension station 34, b-wire to central station,c5, d6, L14, s2, b-wire The calling and audible ringing signals have notbeen mentioned because the invention is not concerned with them.

I claim:

1. Circuits for selecting one station from among a plurality oftelephone extension stations through operation of selection keys at afirst extension station, said circuits comprising an alternating currentsource coupled to rectifier means to provide positive and negativehalfwaves, two speech wires for interconnecting the extension stations,two selecting key contacts (1T, 2T, 3T, 4T) provided in series with eachspeech wire in each extension station, means closing a normally openseparate contact (v1) in response to lifting of a receiver at the firstextension station, said separate contact coupling the positive andnegative half-waves provided by the rectifier means to first terminalsof two pairs of relays (A1, B1, C1, D1), means connecting each pair ofrelays in series between said separate contact and a respective normallyopen relay Contact (u1, u2), means coupling a rectifier (GL3, GL4; GLS,GL6) in parallel with each Of said relays, said rectifiers formingcircuits in phase opposition to each other to serve as by-pass paths forcurrent in different directions so that the half-waves can flow onlythrough one relay and one of the rectiers at a time, closure of aselecting key contact completing a particular path through an additionalrectifier to ground to permit current to fiow through one and only oneof the pairs of relays to operate it and establish the first stage of aconnection to the called extension, closure of a second selecting keycompleting a second -path to establish the connection to the calledextension.

2. Circuits as claimed in claim 1 in which the rectifier means toprovide positive and negative half-waves has the coniguration of arectifying bridge, and a relay (X) which is responsive to thealternating current of the alternating current source is connected inthe diagonal of the rectifying bridge, said relay operating to closeopen contacts for critical circuits When said key contacts are closed.

3. Circuits as claimed in claim 1 in which the means closing thenormally open separate contact (v1) in response to lifting of a receiverincludes an engaging relay (SP) connected to operate as the receiver islifted, said engaging relay closing a plurality of contacts to cause theoperation of a time limit relay (V) and thus close the open separatecontact.

4. Circuits as claimed in claim 3 in which operation of the engagingrelay (SP) closes circuits preparing additional relays for subsequentoperation by closure of the key contacts, said relays including achange-over relay (U), a relay (R) of use in signalling the firstselection, and a relay (S) of use in signalling the second selection.

References Cited UNITED STATES PATENTS 2,278,410 4/1942 Bascom et al.179-18 2,400,148 5/1946 Hubbard et al 179-18 3,328,533 6/1967 Vaccaro etal. 179-18 WILLIAM C. COOPER, Primary Examiner U.S. Cl. X.R. 179-86

